Few oil wells are self-flowing. Most wells must be pumped. Almost all of the wells made to produce by pumping are equipped with sucker-rod activated pumps. In these wells, the pump is installed at the lower end of the tubing string and is actuated by a string of sucker-rods extending down from the surface to the pump. The sucker-rods are attached to a polished rod at the surface. The polished rod extends through a stuffing box and is attached to the mechanical unit which produces the necessary reciprocating motion to actuate the sucker-rods and the pump. Typically, the polished rod is attached at its upper end to a walking beam pivotally mounted to a post. A counterbalancing weight may be directly or indirectly secured to the opposite end of the beam. As the beam is rocked the string of sucker-rods is raised and lowered.
In typical operation the oil in the borehole is pumped out. Then, pumping is discontinued and oil is allowed to seep into the borehole from the surrounding oil-bearing formation. Build-up of oil in the borehole produces a back pressure which impedes the inflow from the formation. Thus, productivity is reduced if the oil in the borehole is not timely removed after accumulating. On the other hand, it is not desirable to operate the pump after the oil level has fallen below the pump inlet. To do so causes physical damage and wearing of the pump.
Past and present practice in oil well pumping involves manually setting electric timers to control the pumping based upon an operator's estimation of the time required to extract the down-hole fluid to a point where no more fluid can be removed. This is known as "pumping off" a well. The disadvantages of this method are excessive wear to down-hole components due to excessive pumping, unnecessary manhours needed to operate the wells and lower fluid production reducing income due to underpumping.
Automatic liquid level monitoring has been proposed wherein acoustical devices are used to sense the depth of the oil within the well. A drawback of this system is that it is affected by foam within the well. Also, it involves complicated mechanical apparatus at the well head. See, for example, U.S. Pat. No. 4,318,298.
The invention disclosed herein relates to oil well pumping and is specific to a method and apparatus which will automatically regulate the pumping of an oil well based entirely upon the detected fluid level in the well. It is an object of this invention to provide a means for automatic well pumping resulting in better recovery of down-hole fluids, increasing production, reducing manhours and down-hole component wear.